Methyl chloride is a toxic gas known to be injurious to humans, attacking the liver, kidneys and CNS. Methyl chloride can be formed as a byproduct during certain chemical reactions. For example methyl chloride is formed during the conversion of a methylamino moiety in a tertiary amine to a urethane using ethylchloroformate. To avoid the hazards associated with a release to the environment when such reactions are run on a commercial scale, it is necessary to employ a scrubbing system to trap the methyl chloride off-gas produced.
One method known for removing methyl chloride as an off-gas involves venting the gas to a reactor containing methanolic KOH. The methyl chloride is converted to methanol or dimethyl ether and KCl by reaction with the KOH. However, this method is inefficient, as the reaction stops after converting only a small portion of the methyl chloride, resulting in release to the environment of the unreacted gas upon disposal of the scrubbing solution.
Another known method for scrubbing methyl chloride involves solubilizing the gas in a continuous stream of methanol. While this method is capable of removing the methyl chloride off-gas, it too is unsatisfactory, requiring the use of large volumes of methanol. In addition, the methanolic solution of methyl chloride thus obtained must be disposed of in a manner that avoids release of the dissolved gas into the environment. Given the relatively low boiling point of methyl chloride (-24.degree. C.), significant amounts of the dissolved gas are likely to escape from solution before it can all be treated.
The scrubbing of methyl chloride, is also described in Canadian Patent No. 1,282,317, via a method which involves contacting the off-gas with a scrubbing liquid comprising a vegetable or marine oil. However, this method is effective only for removal of small amounts of methyl chloride and is unsuitable for scrubbing the quantities of methyl chloride produced by commercial scale reactions.
Methods of destructively scrubbing methyl bromide are also known. In particular, Japanese Kokai JP 49127862 discloses a method involving contacting a solution of methyl bromide in isopropanol with a 20% solution of ethanolamine in water. However, application of methyl bromide technology to the control of methyl chloride emissions is in part impeded by the substantial difference in their boiling points (methyl chloride, -24.degree. C., as compared to methyl bromide, 4.degree. C.). More importantly, the significantly higher chemical reactivity of methyl bromide as compared to methyl chloride precludes direct extension of this technology to the scrubbing of methyl chloride. This is further evident from the absence of any teaching or suggestion in the prior art that such technology can be applied to methyl chloride.